A variety of vessels have been employed in research facilities and medical clinics for the manipulation of material samples. In the biotechnology industry, these types of vessels are standardly referred to as "dilution reservoirs", although these vessels are commonly used for numerous other purposes besides preparing sample and reagent dilutions.
Generally, these can be categorized as being either trough or well type dilution reservoirs. The most basic example of the well type of reservoir is the well-known test tube, which is generally characterized by having a small mouth opening and a long straight neck. The test tube is generally configured to be symmetrical about a central longitudinal axis. The traditional test tube was generally filled by use of a single pipette or squeeze-bulb dropper.
The development of multichannel pipettors allows filling of multiple reservoirs from a single pipettor (also frequently spelled "pipetter"). These usually consist of a parallel array of thin tubes or pipettes controlled by a common handle which can draw and dispense multiple samples of material. Such pipettors typically come with eight or twelve channels and have dispensing tips centered approximately 9mm apart, according to industry standards. Typical industry examples of multichannel pipettors include Finnpippete, T/M; Eppendorf, T/M; Oxford BenchMate, T/M; and Fisher/Wheaton Calibra, T/M.
In response to the development of these multichannel pipettors, systems or arrays of well dilution reservoirs have been made, with rows of tubes bound together in multiples of eight or twelve wells. They may also be formed with square-shaped cross-sections in which the wells may share walls with their neighbors. The individual wells must be reduced in size in order to accommodate the 9mm spacing dimensions of the pipettor tips, thus generally the volumetric capacity of such wells is small unless the depth is increased to an awkward length. Industry examples of well systems designed for use with multichannel pipettors include Corning Well ELISA Plates and Strips, T/M, and Bel-Art Products Mini-Tubes, T/M.
Well type dilution reservoirs have a natural ergonomic disadvantage. In order to dispense material from the multichannel pipettor, the tips of the pipettor channels must be inserted into the relatively small mouths of the well channels, in unison, from a nearly vertical orientation. This can require a very steady hand, and upon repetition, this can become tiring and over lengths of time can lead to complaints of repetitive stress problems such as carpal-tunnel syndrome. Chances of spillage are also increased as the target areas for the pipettor tips are relatively small.
Well dilution reservoirs also have generally small volumetric capacity, as mentioned above, as often as small as 50-250 micro-liters. This small capacity may impede effective mixing of materials if stirring apparatus is difficult to introduce into the cavity, if range of motion of this apparatus is too restricted, or if introduction of stirring apparatus causes concerns of material overflow due to volumetric displacement in these small capacity tubes.
Trough type dilution reservoirs, as the name implies, usually have elongated mouths which have greater length than width. The trough cavities can thus be thought of as having a longitudinal axis, parallel to the length dimension of the mouths and a transverse axis, parallel to the width of the mouths. These trough reservoirs generally provide greater volumetric capacity than the well type reservoirs. There are single reservoirs which can have very large capacities such as 100 milliliters. Trough reservoirs can also have smaller channels which have been grouped together in arrays of eight or twelve, corresponding to pipettor channel configuration. The center to center spacing of the trough mouths may accommodate the standard 9 mm spacing of the multichannel pipettor dispensing tips in a similar way to the arrays of well reservoirs. However, the troughs allow insertion of the pipettor from a greater range of non-vertical approach angles, thus providing an ergonomic advantage over the well type reservoir.
Troughs also have advantages over wells when mixing materials. If mixing is done in a trough prior to distribution to an array of well reservoirs, higher accuracy and precision may be achieved compared to mixing which is done in an array of well reservoirs in which a multichannel pipettor is used to add and then mix materials in the wells themselves. Especially in small volume well reservoirs, small factors such as the presence of bubbles in the pipettor can introduce errors in mixture concentrations. When dealing with small volumes, such errors can more easily constitute a significant percentage of the overall mixture, compared to large volumes of mixture. Small errors introduced into a larger volume mixture may be distributed among the samples, thus making up a smaller, less significant percentage of the overall mixture.
Examples of standard industry trough type reservoirs include Matrix Reagent Reservoirs, T/M; Fisher Multichannel Pipetter Basins, T/M; and E & K Disposable Pipettor Basins, T/M.
Unfortunately, despite the advantages of the trough type dilution reservoir over the well type dilution reservoir, there remain some disadvantages. In applications where very precise quantities of material are to be transferred into and then out of a dilution reservoir, it can be of critical importance that the reservoir contents be capable of complete removal, leaving minimal residue in the reservoir. It is thus important that the reservoir be designed for easy and complete withdrawal of the contents. Previous trough dilution reservoirs often had flat bottoms with no true low point for collection of the contents. Some trough type reservoirs have bottoms which are rounded in a cross-sectional view taken through the cavities' transverse axes, but which are flat as seen in a cross-sectional view through their longitudinal axes. The material will thus tend to accumulate in a line in the bottoms of the cavities along the longitudinal axes. This will make collection of material difficult, as a withdrawal device will need to sweep along this line to collect all the material.
A few previous trough type reservoirs have a low collection point near one end of the elongated mouth, which could facilitate material removal. However, this placement restricts the angle at which this low point can be approached with the pipettor.
Some laboratories perform many material manipulations in the course of a day. This necessitates the use of many dilution reservoirs, which must be either thoroughly cleaned before reuse, or discarded to prevent possibility of contamination of subsequent material. Especially in uses where biological samples are manipulated, sterility of the reservoirs can be a great concern. Disposable reservoirs thus have advantages, as they can be maintained in a sterile condition until use and then discarded.
For reservoirs which are not disposable, choice of material for the unit's composition is very important. A preferred material would have the characteristics of being very inert in contact with biological materials, would have low affinity for sticking or binding of proteins and other materials, and would be easy to sterilize by autoclave or radiation sterilization. Virgin medical grade polypropylene has all of these qualities, and is additionally optically transparent so that a user can readily determine the amount of material in the reservoir.
The high numerical usage of dilution reservoirs in laboratories can make storage space a concern. Thus it will be advantageous if the reservoirs are made to be stackable, thus reducing volume during shipping, for storage before use in the laboratory and for disposal after they have been used.
An optional cover helps to prevent spillage, evaporation of volatile materials, and avoids contamination of reservoir contents.
There is thus a great need for a trough type dilution reservoir which holds enough volume to allow easy mixing of material, is configured with multiple channels which are accessible by multichannel pipettors, allows complete and easily accessible removal of the contents, and is designed for easy ergonomic manipulation of the reservoir material. The reservoir could be even more useful if made to be disposable and stackable, with an optional cover.